We study the impact of an intensive 2.5 years mass media campaign promoting modern contraception in Burkina Faso. Using a clustered randomized design, 16 local radio stations reaching 5.1 million people were randomly allocated either to broadcast the campaign or to the control group. Survey data on 7,500 women, shows the campaign lead to a 5.9 percentage points (20%, p=0.046) increase in the modern contraceptive prevalence rate (mCPR) with the effect concentrated among women with a radio at baseline. Using an individual-level experiment in which 1,500 women were randomly selected to receive a radio, we show that increasing radio exposure in areas reached by the campaign increased contraception uptake by 5.8 percentage point (17.5%, p=0.025). Women who received radios in the control area reduced contraception use by 5.2 percentage points (p=0.025). The campaign worked primarily by providing information on potential side effects of contraception, improving attitudes toward family planning and convincing women already in favor of modern contraception to use it more consistently. Increased contraception translated into reduced fertility and higher self-reported well-being. The campaign had limited impact on fertility preferences. Administrative clinic data shows there were more family planning consultations and contraceptives distributed in treatment areas. Overall, these results demonstrate that an intensive, saturation mass media campaign can significantly accelerate uptake of modern contraception while access to mass media on its own can, in some environments, reduce contraceptive use. We estimate that a nationwide media campaign in Burkina Faso would lead to 225,000 additional women using modern contraception annually at a cost of US$ 7.7 per women.